The long-term objective of this project is to arrive at an understanding of how the nervous system generates behavior and how the neuronal circuits responsible for this function arise during ontogeny. The experimental material on which these studies are to be carried out is the nervous system of leeches, the class of blood-sucking worms belonging to the annelid phylum. The immediate research objectives are as follows: 1) We plan to carry out a neurophysiological and neuroanatomical survey of the giant Haementaria leech now in continuous culture in our laboratory. 2) We plan to analyze the movements carried out by Haementaria embryos at various stages of their embryonic development and to study by electrophysiological means how these movements are controlled by the central nervous system. 3) We plan to carry our neurophysiological and anatomical studies of abnormal leech specimens produced by teratogenic procedures.